Miles per gallon meter

ABSTRACT

This invention relates to an indicating instrument assembly for installation on a vehicle to provide engine performance data to an operator in terms of miles traveled per gallon of fuel utilized. A unique electrical circuit cooperates with means to indicate fuel flow and means to indicate vehicle speed to instantaneously compute and display a miles per gallon information.

United States Patent [151 3,635,079

Tomlinson 51 Jan. 18, 1972 [54] MILES PER GALLON METER PrimaryExaminer-Richard C. Queisser Assistant Examiner-Marvin Smollar [72}Inventor. Nor'vln P Tornhnson, 3162 Sherbrook Alwmey oldham & oldhamDrive, Umontown, Ohio 44685 [22] Filed: Feb. 25, 1970 [21] Appl. No.:14,013 [57] ABSTRACT This invention relates to an indicating instrumentassembly for [52] [1.8. CI M ..73/l14 installation on a vehicle toprovide engine performance dam l MGM!" 15/00 to an operator in terms ofmiles traveled per gallon of fuel utillssl PW 4 -73/1 l4 iud. A uniqueelectrical circuit cooperates with means to indicate fuel flow and meansto indicate vehicle speed to instanl M mm taneously compute and displaya miles per gallon information.

UNITED STATES PATENTS 3,ll8,302 1/1964 Fathauer ..73/ll4 3.376.7374/1968 Timmermans ..73/l l4 6 Claims, 7 Drawing Figures i I L E35?jI3'?J I6 I w l2 F- 1 iSPEEDOMETER 22 I2 VOLTS 33 '0 l 1 i ii i 3 I8 I il I l l i g g as I I I I l I I R i 2 I l 20 l l l I G J m I2 I i FUELPUMP PATENTEDJIIIGIIZ 3.635079 SHEET 1 OF 2 I I I CARBURETOR '6 L Ii/x'z 22 I2 was I 33| EREF E c: o 95 l-Ll 3 FUEL FLOW RATE (F) FIG. 2

FIG. 6 At, c. k I k 60 i E TIME INVENTOR. NORVIN P TOMLINSON t=0 t4 2 BYFIG. 7 ownwav ATTORNEYS PATENTED JAM 8 I972 SHEET 2 [1F 2 RESISTANCE(R0) FUEL FLOW RATE (F) FIG. 5

FIG.3

INVENTOR. NORVIN F? TOMLINSON BY a%.m%

ATTORNEYS MILES PER GALLON METER Heretofore it has been known that therehave been many and various types of instruments and attempts made toprovide a vehicle fuel consumption indication in terms of miles pergallon. Typical of these patents are U.S. Pat. Nos. 3,204,452,3,058,340, 3,246,508, 2,330,159 and 3,253,459. However, these patentsare all objectionable with respect to actual commercial use inincorporation on a standard automobile today because of their complexityand expense, and relative nonadaptability to the average automobile.

Therefore, it is the general object of the invention to avoid andovercome the deficiencies of these prior art patents by providing amiles per gallon indicating device that utilizes commercially availablecomponents, and is easily installed on the conventional automobile andextremely reliable in operation.

A further object of the invention is to provide a miles per gallon meterwhich utilizes a unique mechanical device incorporated with thespeedometer cable to provide a direct indication of speed.

A further object of the invention is to provide a unique miles pergallon meter which utilizes a commercially available flow indicationdevice cooperating with a unique electrical circuit to invert theelectrical output signal therefrom and effect combination thereof withthe speed indication from the speedometer cable.

The aforesaid objects of the invention and other objects which willbecome apparent hereinafter are achieved by providing a miles per gallonapparatus for a vehicle comprising a fuel flow meter to produce anelectrical signal inversely proportional to fuel flow rate, a velocityswitch actuated by the movement of the vehicle to switch in directproportion to the speed thereof, electrical circuit means to combine theinverted electrical signal and the actuation of the switch to produce alinear electrical signal, and meter means driven by said linearelectrical signal.

For a better understanding of the invention reference should be had tothe accompanying drawings wherein:

FIG. I is an electrical circuit diagram of the preferred embodiment ofthe invention;

FIG. 2 is a graphic representation of the electrical output signals E,or E, from the modified fuel flowmeter 10 in the circuit of FIG. 1illustrating the inverse relationship between the fuel flow rate F and[5,;

FIG. 3 is a cross-sectional side view of the speed indication deviceassociated with the speedometer incorporated in the circuit of FIG. I;and

FIG. 4 is a horizontal cross-sectional view taken on line 4 4 of FIG. 3;

FIG. 5 is a graphic representation of the relationship between thevariable resistance of the flowmeter and the instantaneous fuel flowrate to the carburetor;

FIG. 6 is a schematic diagram of a nonlinear potentiometer through whichan output signal E, is generated representing the inverse 1/F of thefuel flow rate F;

FIG. 7 is a graphic representation of charge and discharge currentthrough capacitor C As has been indicated above, the invention relatesto an apparatus for continuously measuring and indicating the fuelmileage of a motor vehicle. Miles per gallon information requires themeasurement of fuel flow rate and the speed of the motor vehicle. Thefuel flow rate is obtained from a fuel flowmeter indicated by the dottedblock number 10 in FIG. 1, which meter 10 is installed in a fuel line 12between a fuel pump 14 and a carburetor 16. although alternatively themeter 10 could be installed between the fuel tank and a fuel pump (notshown). This flowmeter 10 in combination with resistance R, produces anelectrical signal inversely proportional to the rate of flow (in otherwords one over gallons per hour).

The second item which must be measured is vehicle speed (just miles perhour). I preferably accomplished this by inserting a magnetizedarmature, indicated generally by dotted block I8 in FIG. 1, between aspeedometer cable and a speedometer 22. The structure comprising thearmature switch 18 is more fully defined hereinafter, but generally, thearmature activates a reed switch 24 as it rotates to provide vehiclevelocity infonnation.

An electronic circuit comprising the remainder of FIG. 1, and whichcomponents will be more fully described hereinafter, combines the signalfrom the flowmeter 10 with the vehicle velocity information on reedswitch 24 to produce a signal proportional to their product 1(mXm.p.h.-m.p.g.)

This electrical signal is sent to a current meter 26 where it isdisplayed in visual information form for the vehicle operator.

FUEL FLOWMETER ID A fuel flowmeter sensor manufactured by TeleflexMarine of North Wales, Pa., can be modified so that it can be used in myinvention. This sensor by Teleflex Marine, specifically designated as35,090, is a variable orifice type sensor having a resistance whichvaries linearly with fuel flow rate. Effectively the variable resistanceof the flowmeter is similar to a potentiometer. This potentiometer isindicated by resistance R,,. The pickoff point on the potentiometer R,is indicated by arm 32, and its position will depend on the fuel flowrate passing through the sensor. The pickoft' arm 32 will be at point 30for zero flow rate and at point 33 for maximum flow rate.

Because the pickoff position of arm 32 is directly proportional to fuelflow rate, a modification is therefore required in order to obtain asignal inversely proportional to fuel flow rate. This modification isachieved by simply shorting out the bottom section of the potentiometerR, from point 30 to point 31 by a short 35. Thus, the resistance betweenpoint 30 and point 31 will be zero. Point 3l on the potentiometer R isselected to correspond to a flow rate off. The value off is a designconstant, actually equal to about one-half to 1 gallon per hour. Theresistance between point 30 and the pickoff arm 32 is designated as Rand varies linearly with flow rate F for flow rates equal to or greaterthan f. For flow rates less than f, the pickoff arm will be betweenpoint 30 and point 31 and the resistance R, will be zero.

The relationship between R,, and flow rate F is shown in FIG. 5 and isexpressed mathematically as R =m(Ff) for F2] and R O for F51 where F isthe flow rate in gallons per hour through the flow sensor 10, and m isadesign constant relating the change in the resistance R, to the changein flow rate F. The slope of the line in FIG. Sis equal to the value ofm.

A regulated reference voltage E is applied to potentiometer R, at point30 where the flow rate is zero. A resistor R,. whose value is selectedto be equal to the product of at times f, is attached between the pickuparm 32 and ground G. The resistor R, and the resistance R, form avoltage divider network to produce a voltage E, at point 34. Thisvoltage E, is expressed as Substituting the values R,=mf and R,,=m( F-f)into the above equation results in E ,=f Eur! F Thus the voltage (E,) atpoint 34 is a variable voltage and inversely proportional to the flowrate F for flow rates equal to or greater than f. For flow rates lessthan f, the voltage E, is equal to the reference voltage E indicating aflow rate of F. FIG. 2 shows the inverse relationship between the signalvoltage E, and the flow rate Ffor the modified fuel flowmeter.

Another method of modification can be achieved by replacing the linearpotentiometer in the flow sensor with a nonlinear potentiometer R, shownin FIG. 6. Nonlinear potentiometers are made by Markite Corporation. I55Waverly Place, NY. NY. 10014, and Duncan Electronics, Inc. of 2865Fairview Road, Costa Mesa, Calif. 92626. The nonlinear potentiometer Ris made by means of a variable pitch winding or by means of a conductiveplastic in such a manner to produce the desired nonlinear inverserelationship. The pickoff arm 52 on potentiometer R, will depend on thefuel flow rate pasing through the sensor. The pickoff arm will be atposition 50 for zero flow rate and at position 53 for maximum flow rate.Point 51 on potentiometer R, corresponds to the flow rate f describedpreviously. A regulated reference voltage E is attached to potentiometerR, at point 50. The other end, point 54 is attached to ground G. Thevoltage E from the pickoff am 52 is inversely proportional to flow rateF for flow rates equal to or greater than f. For flow rates less than f,the voltage E, is equal to the reference voltage E indicating a flowrate off. This voltage relationship between E, and flow rate F isidentical to the voltage relationship between E, and flow rate F. Thusone curve in FIG. 2 is used to show both voltages E, and E,, as afunction of flow rate.

VELOCITY SWITCH The velocity switch 18 is more clearly shown in FIG. 3.It consists of an armature 40, a two-piece housing 42 and 44 heldtogether by appropriate bolts 46, and a double-throw reed switch 24. Thehole or recess receiving the input speedometer cable is indicated bydotted line 20 with the output connector to speedometer 22 indicated bynumeral 21. The connector 21 is the same as the end of the usualspeedometer cable. The two pieces 42 and 44 are preferably made so thatthey will readily adapt to an existing speedometer cable configurationwhereby the speedometer cable connecting sleeve will be received on malethreads 43 and the male speedometer connection will be directly to thefemale threaded section 45. The armature 40, is preferably made ofplastic and the preferred embodiment has two permanent magnets 48 and 49embedded in its body at 180 relationship to each other as is best seenin FIG. 4. Two magnets are preferably used in the armature since betterdynamic balance of the armature can be obtained than if only one magnetis used. The housing section 42 having a hole 47 formed therein toreceive the reed switch 24 in the sliding relationship illustrated.

The reed switch 24 is a proximity type switch and is activated by themagnets in the armature as the armature rotates. With two magnets in thearmature, the switch will be activated two times for each revolution ofthe armature. The reed switch is held in place in the housing 46 by apotting compound and electrically connected as illustrated in FIG. I tothe overall circuit of the miles per gallon meter. A reed switch such asthose typically made by Hamlin, Inc. of Lake Mills, Wis. 5355 l wouldmeet the objects of the invention.

ELECTRONICS The electronics is shown in FIG. 1. The explanation of thecircuit is as follows: The reed switch 24 is a two position switchmagnetically driven by the automobile speedometer cable. The switchingfrequency is therefore directly proportional to the vehicle speed. Thereed switch 24 allows the capacitor C, to charge in one position(position a) and to discharge through the meter in the other position(position b).

The charge and discharge current through capacitor C, is limited to atolerable amount by the resistance R, in series with the capacitor C,.This average discharge current from capacitor C, is directlyproportional to the product of the voltage E, times the switchingfrequency of the reed switch 24. Since the voltage E, is inverselyproportional to the instantaneous miles per gallon and the switchingfrequency is directly proportional to automobile speed, the readoutcurrent on meter 24 is therefore proportional to the instantaneous milesper gallon or l/GPHXMPH=MPG.

VOLTAGE REGULATOR CIRCUIT The power supply voltage in motor vehicles isunregulated and varies sometimes between 12 and 16 volts. A voltageregulator is therefore required in order to maintain a steady referencevoltage E The voltage regulator contemplated by the invention includes azener reference diode D and resistance R, connected is series betweenground G and the l2 volts input source as indicated in FIG. 1.

CALIBRATION In the production of this item for manufacture, it isdesirable to use inexpensive electronic components. This usually can beachieved by relaxing the tolerance requirements on such parts. A widetolerance on electronic parts usually means an inaccurate measuringdevice. In this case it is very desirable to have a highly accurateinstrument. By means of a calibrating resistor R it is possible to usecomponents with wide tolerances yet have a highly accurate miles pergallon measuring device. The component design procedure is to assume R,is not in the circuit and design the circuit parameters such that thereading on the readout meter 26 for a particular miles per galloncondition is slightly greater than the actual miles per gallon asmeasured by a highly accurate standard flowmeter and an equally accuratespeedometer. Next, R, is connected in the circuit and its resistance isadjusted so that the readout meter 24 reads the correct miles per gallonas established by the highly accurate flowmeter and speedometer. Thecalibrating resistor R acts as a shunt to bypass part of the dischargecurrent around the current meter 26.

CIRCUIT COMPONENT DESIGN The value of the circuit components aredetermined as follows: Assume the calibration resistor R, is not in thecircuit. While the reed switch 24 is in position (a) capacitor C,charges to a voltage [5,. This charge current I is represented by thewaveform from point 60 to point 61 in FIG. 7 and is expressedmathematically as l Iuharle) F: e when The capacitor C dischargesthrough the meter 26 while the reed switch 24 is in position (b).Capacitor C, is a filter to provide a steady reading on the readoutmeter 26.

The average charge current through capacitor C, for each cycle of switchoperation is expressed as where At is the time in seconds for onecomplete cycle of switch operation. Combining the two previous equationsresults in This previous equation can easily be integrated to give Themeter 26 measures the average discharge current, and since the averagedischarge current must be equal to the average charge current, thecurrent through the meter 26 is therefore 'FEI The standard rotationalrate for the speedometer cable of American automobiles is L000revolutions per minute for an automobile velocity of 60 miles per hour.This establishes the following relationship:

Was/3.6, where W is the speedometer rotational rate in revolutions persecond and S is the speed of the automobile in miles per hour.

With two magnets attached to the speedometer cable, as

shown in H68. 3 and 4, the reed switch 24 completes one cycle of switchoperation for one-half rotation of the speedometer cable. Therefore thetime (At) for one cycle of switch operation is Ar=ll2W Combining theabove two previous equations results in Ar-l .8/8 This expression givesthe relationship of automobile speed S to cycle time At of the reedswitch 24. Combining this equation with a previous derived equation (I=E,C,/Ar) gives the following relationship I =E,C SI 1 .8 This equationshows that the current through the meter is proportional to the productof the variable voltage E, and the automobile speed S. Previously it hasbeen shown that the voltage E is inversely proportional to fuel flowrate (E,=f ur/ By combining these above relationships the followingrelationship exists:

The design constants inside the brackets in the above equation establishthe scale factor relationship between miles per gallon and thesensitivity of the current meter. The units .for the above equation areas follows: I is the meter current in microamperes, E is the regulatedreference voltage in volts, C l is the value of capacitance inmicrofarads, f is the flow rate constant in gallons per hour, F is theinstantaneous flow rate through the flowmeter in gallons per hour, and Sis the instantaneous automobile speed in miles per hour. Thus by properchoice of design constants, the reading on the readout meter 26 reads alinear relationship of instantaneous miles per gallon.

For a typical circuit configuration having a l2-volt supply voltage asshown in FIG. 1, the following values would be present for thecomponents illustrated: R 125 ohms; R; 1,000 ohms; R l ohms; R, 20,000ohms; E 6 volts; meter sensitivity 0 to 50 microamperes.

It is true that an error exists in a reading for flow rates less than f.The value off can be made small such that this error occurs only at lowrates. As mentioned previously, the practical value of f would beapproximately to 1 gallon per hour.

Hence, it is seen that the objects of the invention have been achievedby modifying a conventional fuel flowmeter to produce a signal inverselyproportional to fuel flow rate, and combining this with a uniqueelectronic circuit having a speed indication actuating a reed switch toallow the combination to be read directly as a current flow through acurrent meter, with this indication directly indicating miles per gallonfor the vehicle. The unique incorporation of the reed switch into themovement or rotation of the speedometer cable together with theelectrical circuit utilizing this technique achieves the low cost andhighly efficient system of the invention.

While in accordance with the patent statutes only the best knownembodiment of the invention has been illustrated and described indetail, it is to be particularly understood that the invention is notlimited thereto or thereby but that the inventive scope is defined inthe appended claims.

What is claimed is:

l. A miles per gallon apparatus, comprising:

means for producing an electrical signal the voltage of which isinversely proportional to fuel flow rate, the means including a fuelflowmeter;

a capacitor;

meter means for providing a visual indication of miles per gallon; and

a speed switch actuated by movement of the vehicle to switch betweenfirst and second positions in direct relation to the vehicle speed, theswitch connecting the capacitor in charging relation to the means forproducing an electrical signal when in the first position and indischarging relation through the meter means when in the secondposition.

2. Apparatus according to claim 1 wherein the fuel flowmeter has avariable resistance directly proportional to fuel flow rate and whereinthe means for producing an electrical signal further includes circuitmeans associated with the full flowmeter for producing the inverselyproportional signal.

3. An apparatus according to claim 1 which includes means to regulatethe input voltage to the fuel flowmeter.

4. An apparatus according to claim 3 which includes variable resistancemeans positioned in parallel with the meter means to provide calibrationof all circuit components for accuracy of the meter reading.

5. An apparatus according to claim i where the velocity switch comprisesa speedometer cable, an armature interconnected with the cable to rotatedirectly therewith, at least one permanent magnetic means carried by thearmature, a housing surrounding and supporting the armature and thespeedometer cable, and a magnetic actuated reed switch carried in thehousing in proximity to the armature so as to be actuated by eachpermanent magnet upon its rotation thereby.

6. Apparatus according to claim 1 wherein the fuel flowmeter has anonlinear variable resistance to directly produce the electrical signalinversely proportional to fuel flow rate.

1. A miles per gallon apparatus, comprising: means for producing anelectrical signal the voltage of which is inversely proportional to fuelflow rate, the means includIng a fuel flowmeter; a capacitor; metermeans for providing a visual indication of miles per gallon; and a speedswitch actuated by movement of the vehicle to switch between first andsecond positions in direct relation to the vehicle speed, the switchconnecting the capacitor in charging relation to the means for producingan electrical signal when in the first position and in dischargingrelation through the meter means when in the second position. 2.Apparatus according to claim 1 wherein the fuel flowmeter has a variableresistance directly proportional to fuel flow rate and wherein the meansfor producing an electrical signal further includes circuit meansassociated with the full flowmeter for producing the inverselyproportional signal.
 3. An apparatus according to claim 1 which includesmeans to regulate the input voltage to the fuel flowmeter.
 4. Anapparatus according to claim 3 which includes variable resistance meanspositioned in parallel with the meter means to provide calibration ofall circuit components for accuracy of the meter reading.
 5. Anapparatus according to claim 1 where the velocity switch comprises aspeedometer cable, an armature interconnected with the cable to rotatedirectly therewith, at least one permanent magnetic means carried by thearmature, a housing surrounding and supporting the armature and thespeedometer cable, and a magnetic actuated reed switch carried in thehousing in proximity to the armature so as to be actuated by eachpermanent magnet upon its rotation thereby.
 6. Apparatus according toclaim 1 wherein the fuel flowmeter has a nonlinear variable resistanceto directly produce the electrical signal inversely proportional to fuelflow rate.